A major shift in drug abuse epidemiology has been witnessed in North America over the past decade. Although alcohol continues to be widely abused, usage of other substances has proliferated. While addicted individuals share some attributes, certain demographic, psychological, and cognitive characteristics may distinguish alcoholics from those who abuse other substances. This descriptive field study systematically compared the presenting characteristics of alcohol and other substance abusers. Study participants were 208 patients recruited from those beginning treatment for alcohol and drug abuse at two residential, publicly-funded, treatment centers serving French- and English-speaking patients in the greater Montreal region. Subjects were categorized into three groups: alcohol abusers; other drug (principally cocaine) abusers; and both alcohol and other drug abusers. Group differences in age, scores on subscales of the Symptoms Checklist 90, and neuropsychological test scores were all in evidence. Patients in all groups seemed to be experiencing major trauma in their lives. Those who abused only alcohol were older than those also reporting cocaine and other substance usage. Those patients who reported abusing substances either alone or in conjunction with alcohol appeared to be more obsessive-compulsive and exhibited greater hostility. Given such a marked clustering of psychological and cognitive differences across groups, the suitability of a common treatment approach for patients presenting with varied profiles of substance abuse may be questioned. (ABL)